The quality of residuum feeds, particularly heavy oils, suffers from high levels of heteroatoms (nitrogen and sulfur). Such feeds are also high in naphthenic acid contents (measured by total acid number--TAN) which presents corrosion problems in handling (e.g., refineries). These are highly viscous crudes that also possess relatively high densities or low API gravities. Transporting such heavy oils typically requires the blending with costly diluent which reduces the viscosity for pipelining.
Much work has been done utilizing molten caustic to desulfurize coals. For example, see "Molten Hydroxide Coal Desulfurization Using Model Systems," Utz, Friedman and Soboczenski, 51-17 (Fossil Fuels, Derivatives, and Related Products, ACS Symp. Serv., 319 (Fossil Fuels Util.), 51-62, 1986 CA 105(24):211446Z); "An Overview of the Chemistry of the Molten-caustic Leaching Process," Gala, Hemant, Srivastava, Rhee, Kee, Hucko, and Richard, 51-6 (Fossil Fuels, Derivatives and Related Products, Coal Prep. (Gordon and Breach), 71-1-2, 1-28, 1989 CA 112 (2):9527r; and Base-catalyzed Desulfurization and Heteroatom Elimination from Coal-model Heteroatomatic Compounds,"51-17 (Fossil Fuels, Derivatives, and Related Products, Coal Sci. Technol., 11 (nt. Conf. Coal Sci., 1987), 435-8, CA 108(18):153295y).
Additionally, work has been done utilizing aqueous caustic to desulfurize carbonaceous material. U.S. Pat. No. 4,437,980 discusses desulfurizing, deasphalting and demetallating carbonaceous material in the presence of molten potassium hydroxide, hydrogen and water at temperature of about 350.degree. to about 550.degree. C. U.S. Pat. No. 4,566,965 discloses a method for removal of nitrogen and sulfur from oil shale with a basic solution comprised of one or more hydroxides of the alkali metals and alkaline earth metals at temperatures ranging from about 50.degree. to about 350.degree. C.
Methods also exist for the regeneration of aqueous alkali metal. See e.g., U.S. Pat. No. 4,163,043 discussing regeneration of aqueous solutions of Na, K and/or ammonium sulfide by contact with Cu oxide powder yielding precipitated sulfide which is separated and re-oxidized to copper oxide at elevated temperatures and an aqueous solution enriched in NaOH, KOH or NH.sub.3. Romanian patent RO-101296-A describes residual sodium sulfide removal wherein the sulfides are recovered by washing first with mineral acids (e.g., hydrochloric acid or sulfuric acid) and then with sodium hydroxide or carbonate to form sodium sulfide followed by a final purification comprising using iron turnings to give insoluble ferrous sulfide.
The costs for handling such feeds can be exorbitant. Hence, reducing viscosity and naphthenic acid content have become critical targets. Thus, there is a need for low-cost processes which upgrade oils to reduce the dependence on diluent addition and to produce more profitable feedstocks. Other upgrading targets include the reduction of nitrogen and sulfur.